Maharashtra Board Class 11 Biology Chapter 13 Respiration and Energy Transfer PDF Download

Respiration And Energy Transfer

Maintenance of life requires continuous supply of energy.

Respiration fulfills the continuous need of energy.

Teacher's Note

When you run fast, your body needs more energy. Your body breaks down food using respiration to get this energy. Like how a car burns petrol to run.

Exam Trick

Remember: Respiration = Breaking food to get energy. Respiration happens in every cell of your body, all the time.

Points to Remember

Life needs continuous energy supply
Respiration breaks down food molecules
Energy is released in small steps
This energy is stored in ATP molecules
Respiration happens in all living cells

Formation Of ATP

Formation of ATP is called as phosphorylation. In nature, phosphorylation occurs in three different ways.

Photophosphorylation happens in plants during photosynthesis. You already learned this.

Substrate-level phosphorylation is a direct phosphorylation of ADP by transfer of a phosphate group from any suitable substrate. It occurs in cytoplasm of the cells and matrix of mitochondria.

Oxidative phosphorylation is phosphorylation of ADP at the cost of energy released during oxidation of substrates like \(\text{NADH+H}^+\) and \(\text{FADH}_2\). This occurs on the inner mitochondrial membrane only.

When energy is required for any metabolic process, ATP is hydrolysed. ATP hydrolysis releases the energy which is used for the metabolic activities.

Teacher's Note

ATP is like money in your cells. When cells need energy, they use ATP. When ATP breaks, energy is released for work. Like when you spend money to buy food.

Exam Trick

Remember three types: Photo (light) phosphorylation, Substrate level (direct), and Oxidative (using oxygen). Write them down in this order.

Points to Remember

ATP is the energy currency of cells
Phosphorylation is the making of ATP
Three ways to make ATP exist
ATP breaks down to release energy
Energy is needed for all cell work

Anaerobic Respiration

Respiration is a catabolic process wherein complex organic substrate is oxidized to simple components to generate biological energy. Cellular respiration occurs in two different ways as anaerobic and aerobic respiration.

Anaerobic respiration is the cellular respiration that does not involve the oxygen at all. It is also called as fermentation. It is completed through steps like glycolysis and conversion of glycolytic product to any suitable product like lactic acid, ethanol, etc.

Glycolysis

Glycolysis involves the breakdown of glucose molecule into two pyruvic acid molecules. Hence known as glycolysis. This is a common step in anaerobic as well as aerobic respiration. It occurs in cytoplasm of cell. It is completed in two phases as preparatory phase and pay-off phase.

Overall process of glycolysis is completed through ten steps. First five steps constitute the preparatory phase through which glucose is phosphorylated twice at the cost of two ATP molecules and a molecule of fructose 1, 6-bisphosphate is formed. This molecule is split to form a molecule of glyceraldehyde 3-phosphate and a molecule of dihydroxyacetone phosphate. Both of these molecules are 3-carbon carbohydrates (trioses) and are isomers of each other. Dihydroxy acetone phosphate is isomerised to second molecule of glyceraldehyde-3-phosphate. Thus, two molecules of glyceraldehyde-3-phosphate are formed and here, first phase i.e. preparatory phase of glycolysis ends.

In the pay-off phase, both molecules of glyceraldehyde-3-phosphate are converted to two molecules of 1, 3-bisphoglycerate by oxidation and phosphorylation. Here, phosphorylation is brought about with the help of inorganic phosphate and not ATP.

Both molecules of 1, 3-bisphosphoglycerate are converted into two molecules of pyruvic acid through series of reactions accompanied with release of energy. This released energy is used to produce ATP (4 molecules) by substrate-level phosphorylation.

Overall reaction of glycolysis:

\[\text{Glucose}+2 \text{ ATP}+2 \text{ iP} + 4 \text{ ADP} +2 \text{ NAD}^+ \rightarrow 2 \text{ Pyruvate}+2\text{ADP}+4\text{ATP}+2\text{NADH+H}^++2\text{H}_2\text{O}\]

Glycolysis is under tight control. Its rate depends upon the requirement of ATP and many other factors. Glycolytic rate control is achieved by complex interplay between ATP consumption, \(\text{NADH}_2\) regeneration and regulation of various glycolytic enzymes like hexokinase, PFK-1, pyruvate kinase, etc. Besides, it is also controlled by hormones like glucagon, epinephrine and insulin.

Teacher's Note

Glycolysis is like breaking a sugar molecule step by step. Each step releases a little bit of energy. Like walking down stairs one step at a time is easier than jumping.

Exam Trick

Remember: Glycolysis = Glucose breaking. It happens in cytoplasm. It needs 2 ATP to start but makes 4 ATP. Net gain is 2 ATP.

Points to Remember

Glycolysis breaks one glucose into two pyruvate
It has two phases: preparatory and pay-off
It happens in cell cytoplasm
It makes 4 ATP but uses 2 ATP
It works with or without oxygen

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